Southern California’s San Andreas and San Jacinto fault systems are experiencing their highest levels of tectonic stress in at least 1,000 years, according to a new scientific...

A study found parts of the San Andreas and San Jacinto faults are critically loaded after long stress build-up. The findings sharpen planning for a possible linked rupture through Cajon Pass without predicting when a quake will strike.

Tectonic stress along Southern California’s San Andreas and San Jacinto fault systems has reached — and in some areas exceeded — the highest levels seen in the past 1,000 years, according to new research led by Earth scientists at the University of Hawai?i at Ma?noa. Researchers say the system is not showing signs of an imminent rupture, but is operating under unusually high stress in a long-term seismic cycle that could support large earthquakes, including multi-fault events. The study, published in the Journal of Geophysical Research: Solid Earth, suggests the region is in a “critically loaded state,” with stress building across multiple fault segments. One key area of focus is Cajon Pass, a junction between the two fault systems that may act as an “earthquake gate,” either blocking ruptures from crossing between faults or allowing them to link into a single larger event. Lead author Liliane Burkhard, a research affiliate at the University of Hawai?i’s Institute of Geophysics and Planetology and scientist at…